Effect of sulfur content and grain size on the fracture toughness of iron
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90 deg), W. L. PHILLIPS, formerly National Research Council Postdoctoral but after about 2 min, it s p r e a d over the graphite (0 Research Associate, Naval Research Laboratory, Washington, D. C., is 0 deg). F r o m these studies, we concluded that the now with the National Cash Register Company, Dayton, Ohio 45409. p r i m e wetting agent for c r y o l i t e on graphite is a s u r Manuscript submitted June 7, 1972.
Effect of Sulfur Content and Grain Size on the Fracture Toughness
of Iron IN
388-VOLUME 4, JANUARY 1973
METALLURGICAL TRANSACTIONS
in fatigue c r a c k e d s p e c i m e n s . An i n c r e a s e in s u l f u r content is known to c a u s e a d e c r e a s e in the C h a r p y u p p e r s h el f e n e r g y f o r m i l d s t e e l 1'2 and to c a u s e a r e duction in the f r a c t u r e t o u g h n e s s of a h i g h - s t r e n g t h s t e e l . 3 R e f i n i n g the g r a i n s i z e c a u s e s the C h a r p y d u c t i l e - b r i t t l e t r a n s i t i o n to shift to l o w e r t e m p e r a t u r e s . 4'5 T he o b j e c t i v e of this i n v e s t i g a t i o n was to e v a l u a t e the i n f l u e n c e of s u l f u r content and g r a i n s i z e on the fatigue c r a c k e d f r a c t u r e t o u g h n e s s of a p o l y c r y s t a l l i n e F e - M n a l l o y o v e r a r a n g e of t e m p e r a t u r e s . T e n s i l e and c o m p r e s s i v e p l a s t i c flow p r o p e r t i e s of the m a t e r i a l s w e r e also measured. Two f o r g i n g o p e r a t i o n s , conducted at 1370 and 770 K, w e r e u s e d to d e f o r m ingots of f o u r e l e c t r o l y t i c i r o n a l l o y s into r e c t a n g u l a r b a r s . Bend f r a c t u r e s p e c i m e n s , 6 w hich w e r e 1 cm thick by 2 c m d e e p , and c o m p r e s s i o n s p e c i m e n s , which w e r e 0.635 c m in d i a m e t e r by 1.11 c m long, w e r e m a c h i n e d f r o m the f o r g e d b a r s b e f o r e the m a t e r i a l s w e r e r e c r y s t a l l i z e d . T a b l e I g i v e s the m a t e r i a l c o m p o s i t i o n s , the r e c r y s t a l l i z a t i o n p r o c e d u r e s and the r e s u l t i n g g r a i n s i z e s . A f t e r r e c r y s t a l l i z a t i o n , a l l s p e c i m e n s w e r e h o m o g e n i z e d f o r 1 h at 820 K and then c o o l e d at a r a t e of 60 K//h until t h e i r t e m p e r a t u r e s w e r e below 620 K. F a t i g u e c r a c k i n g of the f r a c t u r e s p e c i m e n s was done at 173 K to k e e p the p l a s t i c zone at the c r a c k tip s m a l l . T h e fatigue c r a c k e d b a r s w e r e b r o k e n at a loading r a t e , dK/dt, of 660 M P a " m ~/2" s -1 (660
MN
I
SULFUR
CONT.
Table I. Composition, Recrystallization
Composition, Wt Pct Mn
0.064 0.26 0.072 0.25 0.070 0.25 0.071 0.25
S 0.000
Procedure, and Grain Size
Recrystallization Procedure ......................................... Grain Size, Temp.,K Time,h CoolingRate, K/h pm
930 ( 930 0.011 41250 [1240 0.024 930 0.038 930
3/4 3/4 1 1 3/4 3/4
800 800 * 80
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